1. Field of the Invention
The present invention relates to mechanically balancing the disk pack in a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads coupled to rotating disks. The disk pack rotates the disk surfaces in a hard disk drive. Imbalances in the disk pack adversely affect communication to and from the rotating disk surfaces. Therefore, disk packs must be balanced to minimize rotational variation at the disk surfaces.
The typical prior art disk pack includes a spindle motor, one or more disks, possibly one or more spacers, and a disk clamp. Bolts or screws couple the disk clamp to the spindle motor, acting to clamp the disk(s) and spacers into a rigidly coupled assembly which is rotated by the spindle motor during operation.
Making disk packs includes a rotational balancing process, which mechanically aligns the disk packs by attaching counterbalances. A typical balance tolerance for a disk pack is a variation in angular momentum of 35 milligram-centimeters, as measured by a balance calibration system.
There are several existing approaches to balancing disk packs based upon different counterbalances. These existing approaches have created problems, which have added to the cost of production and/or diminished the reliability of the produced hard disk drives.
A first prior art balancing approach involves altering a symmetric ring coupled to a disk clamp. Cutting, drilling, or punching are used to alter the ring.
A second approach involves drilling one or more holes in either the disk clamp or the spindle motor hub. The spindle motor hub is a spindle motor region containing the screw holes used to couple with the disk clamp when making the disk pack. Machining holes in the disk clamp or the spindle motor hub may introduce contaminants such as machine tailings and machine oils. Furthermore, the machining required is specific to the particular disk pack and must meet narrow tolerances, making this approach expensive.
A third approach involves injecting glue and/or heat sealing plastic at selected spots, and in selected amounts, near the disk clamp to counterbalance the disk pack. This injection releases contaminants, which require cleaning procedures to restore the cleanliness of the disk system when assembled. The injected compounds also require a specific environment in order to harden correctly, further adding cost, and often delays, until the hardening process is completed.
Accordingly, what is needed are counterbalances, and methods of balancing disk packs using such counter balances, which do not require unit specific machining and which do not create contamination problems.